Modern telecommunications offices have evolved in recent years to accommodate greater volumes of traffic, thus placing larger and larger amounts of equipment (usually connected by optical fibers) in areas of limited space. In addition to the increasing numbers of optical fibers, traffic carried by each of the optical fibers is also ever-increasing. As capacity increases, problems arise in the management of the optical fibers of a telecommunication office. Specifically, because optical fibers transport large amounts of high bit-rate traffic, the disruption of such traffic leads to the disruption of service to many circuits and, as such, to many customers simultaneously.
For example, a typical telecommunications office includes a plurality of racks of transmission equipment, each having multiple fiber connections to transmitters and receivers in the line cards supported in the racks. The fibers are ultimately destined for terminals either in that specific office, at customer locations, or in other offices. These office fibers are typically bundled and laid in fiber trays that provide paths or conduits to junction points such as patch panels (e.g., lightguide cross connects) which connect the office fibers (sometimes called “jumpers”) to the outside plant (OSP) fibers which carry traffic from this office to other destinations. Over time, the exact connection paths (i.e., the connection paths between ports on a lightguide cross connect to corresponding ports on the line cards in the racks) may become unknown due to, for example, labels used to identify fibers falling off), fibers being initially labeled incorrectly, or emergency maintenance action requiring a fast response not being properly documented. The unidentified or mis-identified fiber connections can ultimately lead to disastrous Quality of Service conditions. For example, assume that a technician, in the course of responding to a (loss of light) alarm, disconnects a fiber labeled as being connected to a port identified as the source of the alarm. If the fiber connection is mislabeled or unknown, the technician may in fact be disrupting a properly functioning circuit, thus creating a new error and disruption of service and delaying the repair of the original faulted circuit. As such, several means have been proposed for identifying a fiber without interrupting traffic on the fiber connection.
Such proposed means for the identification of optical communication circuits include Local Injection (LI) and Local Detection (LD) methods that have been used in practice for fusion splicing. These techniques involve bending a bundle of optical fibers in a cable at two distant locations and injecting light into the fiber at one bent portion while detecting the injected light that leaks from the fiber at the other bent portion. This method however, has several disadvantages. For example, in order to inject an adequate amount (i.e., power) of light into the coated fiber to be later detected, the fiber must be bent with a curvature large enough (i.e., radius of curvature small enough) to inject light thus causing radiated light of a large power to leak from the bent portion of the fiber to which the LI method is to be applied. This causes deterioration of a signal that is to be transmitted by the bent fiber. Therefore, if the LI method is applied during transmission of an optical signal, troubles such as channel interruption will occur in optical signal communication, and in an extreme case, cracking might occur in the coated fiber. In addition, if light having a power greater than a threshold level is injected into a fiber by the LI method, the injected light may be transmitted to an office or to subscribers resulting in the addition of a noise component that may deteriorate an optical signal being transmitted.
Therefore, a need exists for a method and apparatus for the identification of optical fibers that minimally intrudes with optical signals propagating therein.